The invention relates to a heat-sensitive recording material, particularly a heat-sensitive recording material in which the recorded images can be read with OCR (optical character reader) at a wave-length within the range of 600 to 700 nm.
There have been well-known heat-sensitive recording materials utilizing the colorforming reaction between a colorless or pale colored basic chromogenic material and an organic or inorganic color developer, in which the two colorforming materials are thermally contacted each other to produce recorded images. These heat-sensitive recording materials are comparatively inexpensive and can be used on a recording equipment which is compact and requires fairly easy maintenance. Because of these advantages, the heat-sensitive recording materials have been used not only as the recording medium of facsimiles and various computers, but also in the other various fields.
Recently, the application fields have been variously developed, and the requirements of the heat-sensitive recording material have been increased. As one of them, a heat-sensitive recording material developing black color images which can be read by OCR at a wave length within the range of 600 to 700 nm is required. Generally, basic chromogenic materials having a strong absorbing spectrum at a wave length within the range of 600 to 700 nm develop a blue color. Accordingly, such chromogenic materials are used together with basic chromogenic materials developing a black color to change the developed color to a black tone. However, in a heat-sensitive recording material using such a combination of chromogenic materials, fogging is generated on the white area during the storage. The improvement is strongly required.
An object of the invention is to provide a heat-sensitive recording material which develops a blue black color and in which the following PCS value at a wave length within the range of 600 to 700 nm is 0.8 or more, and each of the whiteness of the background and the color density of the recorded images is not substantially lowered after storing for a long time at high temperature and high humidity. EQU PCS=(R.sub.L -R.sub.D)/RL
R.sub.L : reflective ratio of white bar and margin PA1 R.sub.D : reflective ratio of black bar